IMDs provide therapies to patients suffering from a variety of conditions. Examples of cardial IMDs are pacemakers and implantable cardioverter-defibrillators (“ICDs”). Such IMDs generally monitor the electrical activity of the heart and provide electrical stimulation to one or more of the heart chambers when necessary. For example, pacemakers are designed to sense arrhythmias, e.g., disturbances in heart rhythm, and, in turn, provide appropriate electrical stimulation pulses at a controlled rate to selected chambers of the heart in order to correct the arrhythmias and restore the proper heart rhythm. The types of arrhythmias that may be detected and corrected by pacemakers include bradycardias (slow heart rates) and certain tachycardias (fast heart rates).
ICDs also detect arrhythmias and provide appropriate electrical stimulation pulses to selected chambers of the heart to correct the abnormal heart rate. In contrast to pacemakers, however, an ICD can also provide pulses that are much stronger and less frequent, where such pulses are generally designed to correct fibrillation, which is a rapid, unsynchronized quivering of one or more heart chambers, and severe tachycardias, during which the heartbeats are very fast but coordinated. To correct such arrhythmias, ICDs deliver low, moderate, or high-energy therapy pulses to the heart.
Generally, IMDs are equipped with on-board memory in which data can be stored for later retrieval and analysis via telemetry. Typically, the telemetered signals can provide patient physiologic and cardiac information. This information is generally recorded on a per heartbeat, binned average basis, or derived basis, and involve, for example, atrial electrical activity, ventricular electrical activity, minute ventilation, patient activity score, cardiac output score, mixed venous oxygen score, cardiovascular pressure measures, time of day, and any interventions and the relative success of such interventions. Telemetered signals can also be stored in a broader class of monitors and therapeutic devices for other areas of medicine, including metabolism, endocrinology, hematology, neurology, muscular disorders, gastroenterology, urology, ophthalmology, otolaryngology, orthopedics, and similar medical subspecialties.
Generally, upon detecting arrhythmias and, when necessary, providing corresponding therapies to correct such arrhythmias, IMDs store the data over a set period of time (usually before, during, and after the occurrence of such arrhythmic event). Current practice in the art involves the use of an external communication unit, e.g., an external programmer, for non-invasive communication with IMDs via uplink and downlink communication channels associated with the communication device. In accordance with conventional medical device programming systems, a programming head can be used for facilitating one or two-way communication between IMDs and the external communication device. In many known IMD systems, the programming head can be positioned on the patient's body over the IMD such that the programming head can send wireless signals to, and receive wireless signals from, the IMD.
Implementation and operation of most, if not all, RF communication systems for IMDs and external communication devices involves a balancing or compromising of certain countervailing considerations, relating to such interrelated operational parameters as data transmission rate, transmission range, IMD power consumption and battery life, among numerous others. Such operational parameters are often interrelated in the sense that the adjustment of one operating parameter may permit or require the adjustment of one or more other operating parameters even while predetermined system performance goals and/or requirements continue to be met and predetermined limitations imposed upon operational parameter adjustment are adhered to. For example, to meet a minimum transmission range, the transmitter output power of an IMD must provide telemetry signals having sufficient energy.
Conventional IMDs may employ data retransmission techniques for redundancy and/or to ensure that data is successfully transmitted under poor channel conditions. Some IMDs employ a default retransmission scheme where each transmitted packet or frame is always retransmitted at least once, regardless of channel conditions. Such data retransmission schemes and redundant transmission schemes are somewhat limited in that data is retransmitted even when it is undesirable or unnecessary to do so. Consequently, such IMDs may transmit extraneous telemetry signals, resulting in wasted transmitter output power and decreased IMD battery life.